PHARYNGEAL DERIVATIVES OF AMBLYSTOMA 639 



from the lateral surface of the geniohyoideus muscle; this enters 

 the anterior medial region of the gland and emerges from its 

 posterior medial surface to join the large trunk of the jugular vein 

 some distance caudad. In one instance the venous connection 

 of the gland with the jugular vein is made by a small twig coming 

 from the sternohyoideus muscle. In none of the preparations 

 does the large jugular trunk itself break up to form the complex 

 'rete mirabile' which has befen described by Maurer in Triton 

 alpestris (see his figure 22, a and b) . 



The gland is rarely connected with the carotid artery. In only 

 one case could I trace a small thyreoid artery into the vascular 

 net-work of the gland. Such a condition in Ambly stoma accords 

 with ^laurer's description in Triton. In the live Triton, he 

 showed that the circulation of the blood continued in the gland 

 when, with forceps, he closed the carotid artery just caudad to 

 the gland. On the other hand, he was able to bring the circu- 

 lation to a standstill when he closed the twig of the jugular 

 vein in front before it entered the gland. He therefore concludes : 



dass die Schilddriise der Tritonen in den venosen Kreislauf eingeschaltet 

 ist, eine Thatsache die ich nirgends erwiihnt finde und welche wohl auch 

 fiir die Schilddriise einzig dasteht. Von mechanischem Wert fiir die 

 Blutcirkulation des Kopfes kann dieses Verhalten nicht sein, weil sehr 

 haufig niir ein Ast der Jugular vene diese Wundernetzbildung zeigt. 

 Auch die Ernahrung der Schilddriise leidet nicht darunter, da aus vielen 

 Hautkapillaren Blut, welches somit die Hautathmung durchgemacht 

 hat, in den Stamm der iiusseren Jugularvene iibergeht und somit der 

 Sauerstoffgehalt immer noch era genii gender ist, zumal ja auch das 

 Arterein blut hier ein gemischtes ist. 



It is also probable that it is not necessarj^ that the thyreoid in 

 Amblystoma be connected with the carotid arterj^ in order to 

 carry on its metabolic processes, since the blood in the jugular 

 twig, returning from the capillaries of the skin contain sufficient 

 oxj'gen for the functioning of the gland. 



3. Postbranchial body 



In its development and morphological position, the post- 

 branchial body in Amblystoma is "postbranchial' in the sense 



